The following quote from a book by Dr. Troy Martin, professor of Religious Studies at Chicago's Saint Xavier University, on Paul's letter to the Colossians provides an effective rebuttal to the common but false argument that Paul taught Christian gentiles not to observe the sacred days that were used by the Jews.
"Only by avoiding time-keeping altogether or by adhering to the Jewish calendar [could] the Pauline communities escape idolatrous alternatives. Other time-keeping systems name the days and the months after pagan deities and mark out the seasons by pagan rites.
"In contrast, the Jews distinguish the seasons by festivals that obviously have no pagan connotations. They recognize the months by new moons and name these months using agricultural terms. They designate the week by Sabbaths, and beginning from the Sabbath, they number, instead of name, the days of the week one through six. The only options available to Paul and his communities are Jewish, pagan or no time-keeping system at all, and the evidence indicates they opt for the former.
"The references to time in Paul's Epistle to the Corinthians exclusively reflect the adoption of a Jewish calendar. Even in a place like Corinth, Paul speaks of the first day from Sabbath (. . . 1 Cor. 16:2), not the days of the sun. He builds an elaborate argument based upon the festivals of passover and unleavened bread (1 Cor. 5:6-8) to exhort the Corinthians, 'Let us keep the festival' (1 Cor. 5:8).
"Although the temporal references in Paul's letters are sparse, 1 Corinthians provides strong evidence for the Pauline adoption of the Jewish religious calendar. In addition to 1 Corinthians, the portrait of Paul and Christian communities in the book of Acts demonstrates that the Christians adhered to the Jewish calendar" (By Philosophy and Empty Deceit: Colossians as Response to a Cynic Critique, 1996, pp. 125-127).